Oleksandr Kozachuk
e963e636d3
CI / check (push) Has been cancelled
A recursive Forth word almost always opens with a guard that returns early, so every leaf of the recursion costs a call whose whole body is that test. `Call(self)` now compiles as `<guard> IF <what the guard returns> ELSE Call(self) THEN`, which is what the callee would have done on entry anyway. Half of fib's nodes are leaves: Fibonacci(25) 356 -> 237 us, 1.24x sf64 -> 0.83x, so all five benchmarks now beat it. The guard runs twice along the recursive path, hence the bounds: at most six effect-free operations, at most four call sites, never a tail call. WS-018.
228 lines
11 KiB
Markdown
228 lines
11 KiB
Markdown
# WAFER
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**WebAssembly Forth Engine in Rust**
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An optimizing Forth 2012 compiler targeting WebAssembly. WAFER JIT-compiles each word definition to a separate WASM module and executes it via [wasmtime](https://wasmtime.dev/) (CLI) or the browser's WebAssembly API (web REPL).
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## Highlights
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- **200+ words** across 12 Forth 2012 word sets, all at **100% compliance**
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- **Optimizing compiler** with 6 IR passes + stack-to-local promotion (per region, so a hot loop keeps its registers even inside a word that does I/O; `DO` and `BEGIN` loops alike) + consolidation
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- **Faster than gforth** on all benchmarks in release mode (3-20x), and past SwiftForth `sf64` on all five
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- **JIT compilation** — each `:` definition compiles to its own WASM module
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- **Self-recursive direct calls** — RECURSE compiles to native `call` instead of `call_indirect`
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- **Typed calling convention** — a word with a statically known stack effect passes its stack items as WASM values, so a call keeps them in registers instead of round-tripping through memory
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- **Consolidation mode** — recompile all words into a single optimized WASM module
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- **Interactive REPL** with line editing (rustyline)
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- **Browser REPL** — runs entirely in the browser via wasm-pack + js-sys
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- **Runtime abstraction** — `ForthVM<R: Runtime>` is generic over execution backend (wasmtime or browser)
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## Installation
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Requires [Rust](https://www.rust-lang.org/tools/install) 1.85+ (edition 2024).
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```bash
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cargo install --git https://github.com/ok2/wafer.git wafer
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```
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This installs the `wafer` binary to `~/.cargo/bin/`.
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To install from a local checkout:
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```bash
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cargo install --path crates/cli
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```
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## Usage
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```bash
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# Interactive REPL (type BYE to exit)
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wafer
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# Run a Forth file
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wafer program.fth
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# Pipe input
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echo ': SQUARE DUP * ; 7 SQUARE .' | wafer
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# Consolidation: recompile all words into a single optimized WASM module
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wafer --consolidate program.fth
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# Consolidation with WASM output
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wafer --consolidate -o output.wasm program.fth
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```
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**Example REPL session:**
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```forth
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: FIB DUP 2 < IF DROP 1 ELSE DUP 1 - RECURSE SWAP 2 - RECURSE + THEN ;
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: FIBS 0 DO I FIB . LOOP ;
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12 FIBS CR \ prints: 1 1 2 3 5 8 13 21 34 55 89 144
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VARIABLE COUNTER 0 COUNTER !
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: BUMP COUNTER @ 1 + COUNTER ! ;
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BUMP BUMP BUMP COUNTER @ . \ prints: 3
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```
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## Building from source
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```bash
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git clone --recurse-submodules https://github.com/ok2/wafer.git
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cd wafer
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cargo build --workspace --release
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```
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If you already cloned without `--recurse-submodules`, fetch the Forth 2012 test suite with:
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```bash
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git submodule update --init
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```
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## Performance
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WAFER beats gforth (the GNU Forth reference implementation) on all benchmarks in release mode, and
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SwiftForth `sf64`, which compiles to native code, on all five:
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```
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Benchmark WAFER CONSOL gforth sf64 WAFER/gf WAFER/sf
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Fibonacci(25) 237 242 3340 287 0.07x 0.83x
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Factorial(12)x100K 480 479 6109 1594 0.08x 0.30x
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GCD-bench(20K) 549 541 1830 797 0.30x 0.68x
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NestedLoops(50)x1K 501 509 7092 1898 0.07x 0.26x
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Collatz(2K) 196 190 3955 633 0.05x 0.30x
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```
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Times in microseconds. WAFER/gf < 1.0 means WAFER is faster. CONSOL = after `CONSOLIDATE`.
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Two caveats on the `sf64` column. The SwiftForth build here is x86-64 running under Rosetta 2
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while WAFER and gforth are native arm64, so it is a native-vs-emulated comparison; and sf64
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uses 64-bit cells to WAFER's 32-bit.
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A word whose stack effect is statically known gets a **typed entry point**: its stack items travel in and out
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as WASM values instead of through the memory data stack, so cranelift keeps them in registers across a call
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the way a native Forth keeps TOS in one. The word also keeps a `( -- )` wrapper, which is what the function
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table, `EXECUTE` and the outer interpreter reach, so nothing about the memory ABI changes from the outside.
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Call-heavy code is what this pays for -- Fibonacci went from 4.3x slower than `sf64` to 1.2x. Set
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`WAFER_TYPED_CALLS=0` to fall back to the memory-stack convention.
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Recursive words then get one more thing: their base-case guard is tested at the **call site**, so a
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leaf of the recursion costs a comparison instead of a call. `: FIB DUP 2 < IF EXIT THEN ... RECURSE`
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compiles its `RECURSE` as `DUP 2 < IF ELSE RECURSE THEN`, which is what the callee would have done
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on entry anyway. Half of fib's nodes are leaves, and that is the last 1.4x.
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## Testing
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```bash
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# All tests (~635 currently passing)
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cargo test --workspace
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# Forth 2012 compliance suite
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cargo test -p wafer-core --test compliance
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# Cross-engine comparison (WAFER vs gforth, requires gforth)
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cargo test -p wafer-core --test comparison -- --nocapture --ignored
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# Optimization benchmark report (WAFER-internal)
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cargo test -p wafer-core --test benchmark_report -- --nocapture --ignored
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# Lints
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cargo clippy --workspace
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```
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## Architecture
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```
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Forth Source -> Outer Interpreter -> IR -> [Optimize] -> WASM Codegen (wasm-encoder)
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Runtime trait instantiation
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(shared memory + table)
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/ \
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NativeRuntime WebRuntime
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(wasmtime) (js-sys)
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```
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- **Runtime abstraction**: `ForthVM<R: Runtime>` separates the compiler from the execution engine
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- `NativeRuntime` — wasmtime-based, for CLI, tests, and AOT compilation
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- `WebRuntime` — browser WebAssembly API via js-sys, for the browser REPL
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- **Subroutine threading** via WASM function tables (`call_indirect` for cross-word, direct `call` for self-recursion)
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- **JIT mode**: each new word compiles to a separate WASM module linked to shared memory/globals/table
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- **IR-based pipeline** with 6 optimization passes (peephole, constant folding, strength reduction, DCE, tail call detection, inlining) plus per-region stack-to-local promotion (DO and BEGIN loops, IF/ELSE), DO/LOOP index locals, typed entry points for words with a known stack effect, self-guard expansion, and consolidation
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- **Dictionary**: linked-list word headers in simulated linear memory
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## Project Structure
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```
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crates/
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core/ wafer-core: dictionary, IR, codegen, optimizer, outer interpreter, Runtime trait
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cli/ wafer: CLI REPL, file execution, consolidation
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web/ wafer-web: browser REPL (wasm-bindgen + WebRuntime + HTML/CSS/JS frontend)
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tests/ Forth 2012 compliance suite (git submodule)
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```
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## Forth 2012 Compliance
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Tested against [Gerry Jackson's Forth 2012 test suite](https://github.com/gerryjackson/forth2012-test-suite). 12 of 14 word sets pass at 100%.
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| Word Set | Status |
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| ------------------ | --------------------------------------- |
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| Core | **100%** (0 errors) |
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| Core Plus | **100%** (0 errors) |
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| Core Extensions | **100%** (0 errors) |
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| Double-Number | **100%** (0 errors) |
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| Exception | **100%** (0 errors) |
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| Facility | **100%** (0 errors) |
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| Floating-Point | **100%** (0 errors) |
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| Locals | **100%** (0 errors) |
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| Memory-Allocation | **100%** (0 errors) |
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| Programming-Tools | **100%** (0 errors) |
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| Search-Order | **100%** (0 errors) |
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| String | **100%** (0 errors) |
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| File-Access | Not started (requires WASI integration) |
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| Extended-Character | Not started |
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## Implemented Words
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Over 200 words are implemented across the following categories:
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| Category | Words |
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| ------------ | --------------------------------------------------------------------------------------------------------------- |
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| Stack | `DUP DROP SWAP OVER ROT NIP TUCK 2DUP 2DROP 2SWAP 2OVER ?DUP PICK DEPTH` |
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| Arithmetic | `+ - * / MOD /MOD NEGATE ABS MIN MAX 1+ 1- 2* 2/ */ */MOD M* UM* UM/MOD FM/MOD SM/REM S>D <# # #S #> HOLD SIGN` |
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| Comparison | `= <> < > U< 0= 0< 0<> 0> WITHIN` |
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| Logic | `AND OR XOR INVERT LSHIFT RSHIFT` |
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| Memory | `@ ! C@ C! +! 2@ 2! HERE ALLOT , C, CELLS CELL+ CHARS CHAR+ ALIGNED ALIGN MOVE FILL CMOVE CMOVE>` |
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| Control | `IF ELSE THEN DO LOOP +LOOP I J UNLOOP LEAVE BEGIN UNTIL WHILE REPEAT RECURSE EXIT` |
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| Defining | `: ; VARIABLE CONSTANT VALUE CREATE DOES> IMMEDIATE DEFER` |
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| I/O | `. U. .S CR EMIT SPACE SPACES TYPE ." S" ACCEPT` |
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| Return stack | `>R R> R@` |
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| System | `EXECUTE ' CHAR [CHAR] ['] DECIMAL HEX BASE STATE >IN >BODY ENVIRONMENT? SOURCE ABORT TRUE FALSE BL` |
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| Compiler | `LITERAL POSTPONE [ ] EVALUATE ABORT"` |
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| Parsing | `WORD FIND COUNT >NUMBER` |
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| Exceptions | `CATCH THROW` |
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| Double-cell | `D+ D- D. D.R DNEGATE DABS D= D< D0= D0< D>S 2CONSTANT 2VARIABLE 2LITERAL M+ M*/` |
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| Strings | `COMPARE SEARCH SLITERAL REPLACES SUBSTITUTE UNESCAPE` |
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| Floating-Pt | `F+ F- F* F/ FABS FNEGATE FSQRT FSIN FCOS FTAN FEXP FLOG FMIN FMAX` and 55+ more |
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| Case | `CASE OF ENDOF ENDCASE` |
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| Tools | `WORDS SEE SEE-IR HELP INCLUDE INCLUDED .S F.S ? DUMP MARKER REMEMBER EMPTY GILD BYE` |
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## Web REPL
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Build and run the browser-based REPL:
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```bash
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cd crates/web
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wasm-pack build --target web --out-dir www/pkg
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python3 -m http.server -d www 8080
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# Open http://localhost:8080/
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```
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## Roadmap
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- **File-Access word set** — requires WASI integration for file I/O
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- **Extended-Character word set** — Unicode support
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- **Self-hosting** — minimal Rust kernel (~35 primitives), everything else in Forth
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## License
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MIT OR Apache-2.0
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